The invention relates generally to safety devices for motor vehicles and more specifically, it relates to an inertia activated locking gear for motor vehicle seats of the type where the seat part is supported on a guiding rail assembly for movement in two opposite directions along the longitudinal axis of the vehicle, the rail assembly including supporting rails secured to the floor of the vehicle and a travelling rail slidably supported on the supporting rail and being connected with a position adjustment member that is movable by a displacement device that is stationary relative to the supporting rail.
In a conventional seat of the above-described type the travelling rail of the guiding rail assembly is connected to the lower portion of the seat and is also firmly secured to a toothed rack. The rack meshes with a pinion that is supported for rotation in the base part of the seat and is driven via a worm gear by an electromotor. In order to eliminate the maintenance of the employed worm gears the worm gear is made of a synthetic material. Moreover the worm gears are constructed in such a way that by virtue of their rigidity and their locking moment they are suitable for preventing the seat against displacement nonetheless due to excessive forces occurring in the case of an accident are frequently broken and as a consequence they may completely unlock the longitudinal movement mechanism of the seat and the danger of injury of the user of the seat is considerably increased.